1. Field of the Invention
The present invention relates to an orthogonal frequency division multiplex (OFDM) system, employing pulse shaping and having an enhanced available bit rate, and a method of increasing the available bit rate in a pulse shaped orthogonal frequency division multiplex system.
2. Discussion of the Background
One of the key issues when designing a third generation multiple access system is the need to support high bit rates, see for example P. Willars, "Key Issues for a 3.sup.rd Generation Multiple Access Concept". In a multiple access system based on OFDM, the signal has to be pulse shaped in order to suppress the side lobes and reduce the size of the neighboring guard bands. Unfortunately, pulse shaping breaks orthogonality on every other sub-carrier and reduces the available bit rate (on a link level) by a factor two. The present invention enables recovery of the lost orthogonality, thus making it possible to transmit data with the full bit rate and suppressed side lobes. This results in only a slight loss in performance.
Where there is a demand for high bit rates, this will reduce system capacity (in terms of the number of users per cell). If the system capacity is to be increased there will be a need for increased in infrastructure investment, see C. Ostberg, "Coupling Losses, Coverage Range and Spectrum Mask Requirements". Therefore, it is very important for OFDM systems to support high maximum and highly variable bit rates in a single cell. In comparison with other transmission technologies, OFDM systems demonstrate that they can support the highest bit rates, see for example, P Willars, "A Comparison of Multiple Access Concepts".